Over-lithiated Cathode Material for Lithium Loss Compensation
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Solution Overview
Problem
Conventional lithium-ion batteries experience irreversible lithium loss due to conversion reactions and solid electrolyte interphase formation, leading to decreased specific energy and power, which current compensation methods like electrochemical lithiation or in-cell lithiation are costly and inefficient.
Innovation Solution
The use of over-lithiated positive electroactive materials, such as LixMn2O4 or LiMn(2−x)NixO4, in combination with silicon-containing negative electrodes, which maintain high Columbic Efficiency to mitigate lithium loss and enhance cycle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lithium-ion batteries are used with standard cathode materials, then the battery can operate with typical capacity, but irreversible lithium loss occurs due to conversion reactions and SEI formation, leading to decreased specific energy and power
Solution Approach 1:
The cathode material is pre-lithiated during synthesis to contain excess lithium that compensates for irreversible lithium loss occurring during the first charge cycle. This preliminary addition of lithium ensures that the battery maintains its designed capacity despite subsequent lithium consumption in SEI formation and conversion reactions.
Solution Approach 2:
The stoichiometric ratio of lithium to cathode material is modified by using excess lithium precursors (such as Li2CO3, LiOH, or Li2SO4) during synthesis, creating cathode materials with formulas like Li1.1Mn2O4 or Li1.3Mn2O4. This parameter change in composition directly addresses the lithium loss problem by providing a lithium reservoir.
2Use of energy by moving object
If over-lithiated cathode materials are used to compensate for lithium loss, then specific energy and power are improved, but the cathode material composition becomes non-stoichiometric requiring special synthesis methods
Solution Approach 1:
The synthesis process is modified by adjusting the stoichiometric ratios of precursors to incorporate excess lithium into the cathode structure. Common lithium-containing additives like Li2CO3, LiOH, or Li2SO4 are used in controlled amounts during co-precipitation or solid-state synthesis to achieve the desired over-lithiated composition without requiring complex post-processing steps.
Solution Approach 2:
The excess lithium is incorporated into the cathode structure during the standard synthesis process itself, rather than requiring separate lithiation steps. The synthesis methodology automatically integrates the additional lithium into the crystal lattice, simplifying manufacturing by combining multiple functions into a single process step.
3Quantity of substance
If silicon-containing negative electrodes are used to increase capacity, then energy density is enhanced, but first cycle lithium loss increases due to conversion reactions and SEI formation
Solution Approach 1:
The cathode material is designed with excess lithium capacity from the outset to counteract and compensate for the lithium that will be irreversibly consumed during silicon anode SEI formation and conversion reactions. This preliminary compensation ensures that the battery achieves its target capacity despite the silicon anode's high initial lithium consumption.
Solution Approach 2:
The N/P ratio (negative to positive electrode capacity ratio) is adjusted by increasing the effective lithium capacity of the cathode through over-lithiation, rather than reducing the silicon anode capacity. This parameter change maintains the high energy density benefit of silicon while compensating for its lithium consumption through cathode composition modification.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in improved energy density and reduced capacity loss over time, with specific energy and power enhancements, as demonstrated by increased energy density in example cells.
Implementation Method 1
Such lithium ions may be assimilated into the material of the positive electrode by an electrochemical reduction reaction
Implementation Method 2
the negative electrode may contain a comparatively high concentration of intercalated lithium, which is oxidized into lithium ions and electrons
Implementation Method 3
Lithium ions may travel from the negative electrode to the positive electrode, for example, through the ionically conductive electrolyte solution contained within the pores of an interposed porous separator
Data Source
AI summary
The present disclosure relates to over-lithiated positive electroactive materials for use within an electrochemical cell. For example, the electrochemical cell includes a positive electrode that includes an over-lithiated positive electroactive material that includes one of LixMn2O4 (where 1.05≤x≤1.30) and LiMn(2−x)NixO4 (where 0≤x≤0.5). The electrochemical cell can include a negative electrode that includes a silicon-containing negative electroactive material having a Columbic Efficiency greater than or equal to about 80% and less than or equal to about 90%.